Stereoselective synthesis of trans-3-functionalized-4-pyrazolo[5,1-b]thiazole-3-carboxylate substituted beta-lactams: Potential synthons for diverse biologically active agents

An efficient protocol for the stereoselective synthesis of pyrazolo[5,1-b]thiazole-3-carboxylate tethered beta-lactam conjugates 8a-j from novel pyrazolo [5,1-b]thiazole-3-carboxylate substituted Schiff's bases 6a-f is reported here. The reaction between various ketene precursors and novel Schiff's bases 6a-f afforded exclusive formation of trans-beta-lactams 8a-j. The substrate scope of this approach was investigated extensively by varying different groups (R, Z). All the novel compounds were characterized using various spectroscopic techniques, such as FT-IR, H-1 NMR, C-13 NMR, elemental analysis, C-13 NMR (DEPT-135), and mass spectrometry in representative cases. Single crystal X-ray crystallographic study of trans-ethyl 7-(1-(4-methoxy-phenyl)-4-oxo-3-phenoxyazetidin-2-yl)-6-methyl-2-(methylthio)pyrazolo[5,1-6]thiazole-3-carboxylate 8a has confirmed the molecular structure and the stereochemical outcome. To the best of our knowledge, the synthesis of such types of Schiff's bases and beta-lactam conjugates has not been reported so far. [GRAPHICS] .